As evident from the widespread use of cellular phones, pagers, personal digital assistants (PDA's), wireless laptop computers, and a varied assortment of other data and communications devices—the World has evolved into a highly connected society. Despite the abundance of devices for transmitting and receiving information, there are connectivity related problems between the individual devices as well as the underlying infrastructures employed in the transmission and reception.
The inability of wireless devices tends to be related to the specific implementation utilized in the design. Thus, while the general hardware elements are similar, the design limits the usage to a very particular deployment. For example, cellular phones tend to be protocol specific, so a person that switches from Sprint PCS cellular service to another provider will have to replace the entire phone. Other devices suffer from the same difficulties, and accessories and other implementation schemes have to be used to provide interconnectivity.
A proposed solution to the non-standardized communications operations lies in the software defined radio (SDR) architecture. In general, software defined radios (SDRs) is used to describe radios that provide software control and reconfiguration of a variety of modulation techniques, wide-band or narrow-band operation, communications security functions (such as hopping), and waveform requirements of current and evolving standards over a broad frequency range. The frequency bands covered may still be constrained at the front-end requiring a switch in the antenna system.
Since the initial developments in the early 1990's, researchers have been feverishly working on making SDR a reality. As stated, a software defined radio is a radio whose channel modulation waveforms are defined in the software. Waveforms are generated as sampled digital signals, converted from digital to analog via a wideband digital to analog converter (DAC) and possibly upconverted from an intermediate frequency (IF) to a radio frequency (RF). On the receiver end, a wideband Analog to Digital Converter (ADC) captures all of the channels of the software radio node. The receiver then extracts, downconverts and demodulates the channel waveform using software on a general purpose processor. By employing common hardware elements and implementing design changes via the software, the end-user obtains a seamless transition between various protocols and the life cycle of the device is greatly enhanced.
SDR is an enabling technology applicable across a wide range of areas within the wireless industry that provides efficient and comparatively inexpensive solutions to several constraints posed in current systems. For example, SDR-enabled user devices and network equipment can be dynamically programmed in software to reconfigure their characteristics for better performance, richer feature sets, advanced new services that provide choices to the end-user and new revenue streams for the service provider. SDR is uniquely suited to address the common requirements for communications in the military, civil and commercial sectors.
There are various types and implementations of SDR architectures, such as modal SDR and reconfigurable SDR, depending upon the application. There are practical considerations related to cost, size, power, and weight to contend with in addition to the performance characteristics desired.
A basic block diagram of the SDR functional blocks is shown in prior art FIG. 1. As the goal is to employ generic functional hardware blocks, the interface and internal processing becomes important. There are various high-level hierarchical functional models for SDR systems. In general, there are four functional areas that need to be addressed by the SDR, namely front end processing 50, information security 30, information processing 25, and control 35.
Front end processing 50 refers to input/output (I/O) interface, the front-end RF processing, the RF/IF up/down conversions and the change between digital and analog signals. Modulation/demodulation processing is considered part of the front end processing.
In a typical scenario, an antenna 5 is coupled to the RF section 10. The antenna 5 is for both transmission and reception in conjunction with the RF section 10 for those applications requiring both transmission and reception. The RF section 10 is well known in the art and generally encompasses diplexers, amplifiers and filters. The diplexer is a type of switch that allows a single antenna to transmit and receive signals, whereas other designs employ separate antennas for transmitting and receiving. For reception, the antenna 5 typically feeds an input signal to an amplifier stage to boost the signal to acceptable levels. The IF section 15 usually employs one or more mixers to downconvert the RF signal to the IF frequency by mixing the RF signal with the local oscillator signal and using the difference signal as the IF. Filtering can be used to extract known noise or unwanted/extraneous signals along with multiple mixer and amplification stages.
The DAC/ADC stage 20 is used to convert digital-to-analog and analog-to-digital processing. For received signals, the analog IF signal is coupled to an analog to digital converter (ADC) converter converts the analog signal to digital samples that is then digitally processed in the baseband section by some processing engine 25. The signal processing extracts the information signals which are then delivered to the appropriate function via an interface connection.
Information security 30 is employed for the purpose of providing user privacy, authentication, and information protection. In the commercial environment, this protection is specified by the underlying service standard while in the military arena this protection is consistent with the various Governmental doctrines and policies in effect.
A processing engine 25 is used for information processing for decomposing or recovering information signals containing data, control, and timing. Content processing and I/O functions map into path selection (including bridging, routing, and gateway), multiplexing, source coding, signaling protocol, and I/O functions.
The SDR architecture is designed to support functions connected through open interfaces, and procedures for adding software specific tasks to each of the functional areas. The software applications for the open architecture consist of multiple subsystems interconnected by open interfaces, wherein the subsystems are determined by implementation considerations. Each subsystem typically contains any required hardware, resident firmware, an operating system, and software modules that may be common to more than one application. Interfaces link the software application to specific modules within each subsystem. The application layer tends to be modular, flexible, and software specific, with a common software API layer.
The functional interface of the SDR architecture has interfaces that are implementation dependent with data and information traffic exchanged between the functional blocks along the interfaces. The interfaces can be described as information and control oriented with control over each of the functional blocks. The information transfer, control and status data is between the various functional blocks including the antenna, RF section, IF section, processing engine, security section, and control interface. As an example, frequency at which a wireless signal is generated is determined the RF section and can be changed to accommodate different operating environments such as moving between regions with different frequency assignments.
SDR is more easily implemented in wireless devices and the handheld devices employing SDR generally have performance limitations that are dependent on the battery power, size, weight, and cost requirements. Implementing SDR into laptops and automobiles present differing criteria but using the underlying principles.
One example of the potential for SDR lies in the wireless cell phone area. Existing communications network, such as cellular, use radios to operate with a specific wireless data network. As a user travels outside of the coverage area of its chosen wireless data network, the radio signal is lost. Although some wireless data networks have established cooperative roaming agreements that allow a user with a compatible radio design to operate on a second, foreign wireless data network. But, the roaming agreements only help to alleviate coverage limitations and cannot provide for seamless, widespread operation due to the existence of wireless data network incompatibilities.
Current wide area wireless voice and data networks communicate using different technologies, such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Global System for Mobilization (GSM), Cellular Digital Packet Data (CDPD), DataTac, Mobitex, and General Packet Radios Service (GPRS). The utilization of various frequency bands also segregates wireless networks. While portable radio devices have emerged offering limited operation on multiple frequency bands, few commercial devices have been realized that can provide multiple communication modes. Thus, when a user enters a region serviced by a non-compatible wireless data network, the user may need to either rent or purchase a radio that is compatible with that region's local network.
Existing cellular radios commonly communicate via a single cellular service, for example, analog, Personal Communication Service (PCS), CDMA, TDMA, GSM, or Iridium service. The radio typically communicates by generating and receiving a waveform that is fixed throughout the lifetime of the radio. A problem with such a radio is that when a user moves from a “home” location to a “remote” location, the radio is not easily configurable to communicate at the remote location, as that location has coverage via a different service. For example, when a user travels overseas, the user's radio does not support a service that is available at the home location. In such situations, the user may need to, for example, rent or purchase a radio that is compatible with local communication equipment.
Another problem is when existing radios need to update or receive a software application (e.g., wireless email, operating system). Typically, a radio is taken into a service center to update or receive an application so that the radio can provide a service associated therewith, which is time consuming and expensive.
Frequently, users of radios such as police, federal agency, and military encounter difficulties when attempting to interoperate communication equipment. For example, when a representative from the Federal Bureau of Investigation (FBI) travels to a remote location, the representative may need to borrow equipment from regional officials to communicate with local police and fire services. This problem was identified and initiatives under the Homeland Defense legislation are seeking to improve communications between various domestic agencies. Similarly, in the military community, a Navy ship may desire, for example, to make and receive phone calls at a port at a remote location via local infrastructure equipment. Frequently, existing systems do not allow interoperability between military and local communication equipment. Thus, a problem with existing systems is interoperability between communications equipment, and the additional complexity and expense to “translate” from one communication technique to another.
Another problem with existing radios, including original manufactured and those serviced/repaired, is verifying when a radio meets a predetermined specification for communications. For example, when the Federal Communication Commission (FCC) needs to validate that a radio meets a predetermined specification (e.g., noninterference, splatter, noise, out-of-band noise) a method to verify the specification is needed to ensure a radio operates according to regulatory restriction. In other words, the FCC needs to verify the performance for different types of radios within predetermined specifications when performing communication operations.
The SDR technology enables flexible radio systems with multi-serviced, multi-standard, multi-band operation via re-configurable and re-programmable software instructions. The flexibility of a software defined radio derives from the ability to operate in a multi-serviced environment without being constrained to a particular standard but able to offer services in an already standardized or future system, on any radio frequency band.
The basic concept is based on the use of a simple hardware platform built using SDRs to enable customers to modify both the network and the end-user device to perform different functions at different times. It performs the majority of signal processing in the digital domain using programmable DSPs and hardware support, but some signal processing is still done in the analog domain, such as in the RF and IF circuits. There are numerous implementations utilizing the SDR architecture. For example, one variation has the antenna connected directly to an ADC/DAC converter and all signal processing is done digitally using fully programmable high speed DSPs. In general, the SDR architecture permits all functions, modes, and/or applications, to be reconfigurable via software. Such a system in flexible, reduces obsolescence, enhances experimentation, and brings together the analog and digital environments.
Devices that implement SDR technology are programmable, have multiband/multimode capability, provide simultaneous voice, data, and video and offer full convergence of digital networks and radio science. Such smart radios configure themselves to perform the communications task requested using different frequency bands, modes, etc., and even selecting the optimal communications format. The processing system of the radio can include cognitive functions that learn about the operating environment such as other users nearby, interference, location, and elevation, to be optimally configured to maximize efficiency and reduce interference.
End-users have greater choices and can easily implement “pay as you go” features. There is device independence with scalable hardware that enhances compatibility on a global scale. The manufacturers and also reap great benefits by reusing stock hardware and having lesser number of models. The network providers simply service offerings without having to support a large number of different protocols and standards.
The SDR concept spans all types of wireless handhelds from cellular phones to feature phones, smart phones, PDAs, computing devices and even smart appliances. The most prominent and immediate area of adoption is in the communications field. Today's digital cellular and PCS networks use a variety of second generation (2G) digital technologies for the air interface link between the terminal and network and embrace a number of standards (e.g. GPRS, HSCSD etc.) and protocols (WAP, pJAVA, compact_html etc.) for accessing the Internet. The divergent 2G standards (adopted by large groups of end-users around the globe) often frustrate business travelers who communicate with their customers or offices while traveling from one network type to another as they cannot use the same device without significant enhancements/adjustments to deal with incompatible systems. To add to the complexity, the wireless industry is in the throes of migrating to next generations of these standards, as well as introducing technologies such as GPS (for location services), Bluetooth (for local communications), and the like. SDR offers the ideal solution to accommodate the many standards, frequency bands and applications by offering end-user devices that can be programmed, fixed or enhanced by over-the-air software. With SDR, one would implement a common hardware platform and accommodate these standards and technologies via software modules and firmware.
Due to the theoretical advantages being proposed for SDR, several groups from the commercial, civil, military and academic areas have implemented studies through cooperative research. There is even a forum for SDR that brings together major players from around the globe to attempt to establish a common framework and to cooperatively integrate the concepts into current and evolving commercial standards. The goal of the industry is to lower the development cost and cost of ownership of wireless communication equipment. The US and many international governments and numerous commercial companies are seeking to implement all signal processing for a wireless device in software. Thus any change to the modulation, equalization, or bandwidth, is simply a software upgrade to the system.
SDR enhances and extends the capabilities of current and proposed wireless standards and serves as an enabler of choice as well for Internet concepts and business models in the wireless industry. In each of the major market sectors, Commercial, Military and Civil, SDRs enable new applications as described herein. In particular, some of the benefits include: True international connectivity; Portable Command Station for crisis management; Secure, encrypted Location awareness; Inter-agency communications when desired; Mission reconfigurability; “Freedom of Choice”—applications, band/protocols; MP3AM/FMMedia Distribution; Interactive betting; CD quality music; Instant routing of emergency information; Options to select communications channel by availability; Virtual private network-Closed user groups; Real-time flexibility; Media Distribution; Portable Command Post; Combined delivery of e-mail, voice mail, messages and FAX; Integrated radio, router, computer; Browser malleability; International connectivity to prevailing networks.
The SDR Forum has been working closely with global standards bodies and other industry groups such as RAST, 3GPP and ANSI to develop the standards for bringing SDR to full commercial viability. There are many published materials related to SDR and various designs and proposals of operation, however there is still a general disagreement as to the optimal form, features, or unifying standard. In the article Universal Platform for Software Defined Radio, as well as the corresponding patent application WO 02/05444A1, the general background is well described.
U.S. Pat. No. 6,052,600 discloses a software defined radio which communicates with a base station to receive valid operation licenses and appropriate software configuration instructions in order for the radio to communicate over a plurality of wireless data networks. If the system is unable to obtain sufficient information from a base station prior to losing a current wireless data network connection, the radio is not able to dynamically select a new software configuration and wireless data network without directions from the base station.
In U.S. Pat. No. 6,526,110 there is disclosed a device that receives and demodulates digital signals encoded in multiple formats. The apparatus includes multiple processor units and a memory embedded with the processor units, and a cache connected to each of the processor units. The cache for communicating between the plurality of processors. The embedded memory can include data and instruction memory. The processor units and memory are configured as a multi-mode receiver demodulator front-end capable of receiving digitally modulated signals in multiple formats, and demodulating the signals in real-time in response any one of the multiple formats.
In U.S. Pat. No. 6,181,734 a software defined radio is disclosed in which different waveforms may be utilized. The radio includes a memory (801) in which software (802, 805, 806) for specific waveforms is stored. The radio further includes one or more processors (807, 809, 811) which extract waveform specific software to process information for transmission or reception. All processing of the information between reception or reproduction of speech and transmission and reception of radio frequency signals, respectively, is performed in software.
Thus, there are enormous benefits to the widespread use of SDR technology in portable communications devices. The prior references demonstrate the practicality of using reconfigurable signal processing and computing resources to implement a SDR, and there have been some forays into commercialization. However, despite all the attempts in the art, there has yet to emerge a scheme that fulfils the industry requirements and addresses all the aforementioned problems. What is needed is a system that provides the standardized building blocks for SDR such that the scheme is flexible, easy to implements, cost-effective, and alleviates the problems known in the art such that it is accepted by the industry at large.